As Red has already said, you are fine to take a test now as some can test from four days prior to an expected period, although they are not as accurate when taken at this time. Also, all of the symptoms you describe could be period signs, and feeling sick (or not) is nothing to go by - I didn't get morning sickness atall throughout my pregnancy, it doesn't mean I wasn't pregnant though!
If you intend doing one at lunchtime buy one of those double packs, as tests are more accurate when done first thing in the morning so it might be worth doing another tomorrow morning as well as the one at lunchtime.
Post back and let us know how it goes, the people on here are very helpful and I'm sure would offer great advice whatever the result.